Ultrasonic imaging apparatuses play an important role in current medical care. This is because the apparatuses are smaller in scale than other medical diagnostic imaging apparatus including X-ray diagnostic apparatuses and MRI (Magnetic Resonance Imaging) apparatuses, and the apparatuses can display e.g. motions of objects to be inspected such as pulsing motions of hearts and motions of fetuses in real time by simple operation of only applying ultrasonic probes to body surfaces.
Specifically, the ultrasonic imaging apparatus respectively supplies drive signals to a plurality of vibrating elements contained in the ultrasonic probe, and thereby, transmits ultrasonic wave into a test object. Then, the ultrasonic imaging apparatus respectively receives reflected wave of the ultrasonic wave generated by differences in acoustic impedance among living tissues by the plurality of vibrating elements, and generates an ultrasonic image based on the reflected wave received by the ultrasonic probe.
Here, in the ultrasonic imaging apparatus, to improve image quality of the ultrasonic image, control of delay times is performed on drive signals supplied to the plurality of vibrating elements and reflected wave signals respectively obtained from the plurality of vibrating elements.
Specifically, the ultrasonic imaging apparatus controls times of the drive signals supplied to the respective vibrating elements using the delay times in response to distances between a predetermined focal point within the test object and the respective vibrating elements, and thereby, transmits ultrasonic wave beam-formed on the predetermined focal point of the test object. Then, the ultrasonic imaging apparatus synchronizes and adds (phases and adds) the signals from the predetermined focal point received at different times in the respective vibrating elements using the delay times in response to the distances between the predetermined focal point within the test object and the respective vibrating elements. Thereby, the ultrasonic imaging apparatus generates one focused received signal.
As described above, in order to synchronize the respective signals from the predetermined focal point, an analog or digital delay circuit is required. For example, PTL 1 discloses a configuration for delaying by series-connecting sample holding means and a plurality of capacitor memory circuits, and, at a constant sample frequency, delaying with respect to each sampling cycle in the capacitor memory circuits and controlling a hold time of the sample holding means for shorter delays equal to or less than the sampling cycle. Further, PTL 2 discloses an ultrasonic diagnostic apparatus that performs reception delay time control by digital processing for reducing a circuit scale and manufacturing cost.